U.S. patent application number 13/520454 was filed with the patent office on 2013-03-21 for display assembly comprising a glass-ceramic plate.
This patent application is currently assigned to EUROKERA S.N.C.. The applicant listed for this patent is Michael Bourgeois, Bertrand Charpentier, Jean-Philippe Mulet, Pablo Vilato. Invention is credited to Michael Bourgeois, Bertrand Charpentier, Jean-Philippe Mulet, Pablo Vilato.
Application Number | 20130070451 13/520454 |
Document ID | / |
Family ID | 42546282 |
Filed Date | 2013-03-21 |
United States Patent
Application |
20130070451 |
Kind Code |
A1 |
Mulet; Jean-Philippe ; et
al. |
March 21, 2013 |
DISPLAY ASSEMBLY COMPRISING A GLASS-CERAMIC PLATE
Abstract
Display assembly 1 comprising, on the one hand, a glass-ceramic
plate 2 of the lithium aluminosilicate type, the optical
transmission of which for a thickness of 4 mm is between 0.2% and
4% for at least one wavelength between 400 and 500 nm and, on the
other hand, a luminous device 4, characterized in that the luminous
device 4 comprises at least one polychromatic light source 5 having
at least a first emission of nonzero intensity at said wavelength
between 400 and 500 nm and at least a second emission of more than
500 nm, and such that the positioning of said source 5 is designed
to allow display through said glass-ceramic plate 2.
Inventors: |
Mulet; Jean-Philippe;
(Montreuil, FR) ; Charpentier; Bertrand;
(Chateau-Thierry, FR) ; Vilato; Pablo; (Paris,
FR) ; Bourgeois; Michael; (Paris, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mulet; Jean-Philippe
Charpentier; Bertrand
Vilato; Pablo
Bourgeois; Michael |
Montreuil
Chateau-Thierry
Paris
Paris |
|
FR
FR
FR
FR |
|
|
Assignee: |
EUROKERA S.N.C.
Chateau-Thierry
FR
|
Family ID: |
42546282 |
Appl. No.: |
13/520454 |
Filed: |
November 30, 2010 |
PCT Filed: |
November 30, 2010 |
PCT NO: |
PCT/FR10/52568 |
371 Date: |
July 3, 2012 |
Current U.S.
Class: |
362/231 |
Current CPC
Class: |
C03C 10/0027 20130101;
F21V 1/02 20130101 |
Class at
Publication: |
362/231 |
International
Class: |
F21V 1/02 20060101
F21V001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 21, 2010 |
FR |
10 50387 |
Claims
1. A display assembly, comprising a glass-ceramic plate comprising
a lithium aluminosilicate and, a luminous device comprising a
polychromatic light source, wherein: an optical transmission of the
glass-ceramic plate for a thickness of 4 mm is between 0.2% and 4%
for at least one wavelength between 400 and 500 nm; the
polychromatic light source has at least one first emission of
nonzero intensity at said wavelength between 400 and 500 nm and at
least one second emission at a wavelength of more than 500 nm; and
the polychromatic light source is positioned to allow display
through said glass-ceramic plate.
2. The display assembly of claim 1, wherein an optical transmission
of the glass-ceramic plate, for a thickness of 4 mm, is between
0.4% and 1.5% for at least one wavelength between 400 and 500
nm.
3. The display assembly of claim 1, wherein the glass-ceramic plate
comprises in percentages by weight: TABLE-US-00005 SiO.sub.2 52-75%
Al.sub.2O.sub.3 18-27% Li.sub.2O 2.5-5.5% K.sub.2O 0-3% Na.sub.2O
0-3% ZnO 0-3.5%.sup. MgO 0-3% CaO 0-2.5 BaO 0-3.5%.sup. SrO 0-2%
TiO.sub.2 1.2-5.5% ZrO.sub.2 0-3% P.sub.2O.sub.5 0-8%.
4. The display assembly of claim 1, wherein the glass-ceramic plate
comprises, in percentages by weight: TABLE-US-00006 SiO.sub.2
64-70% Al.sub.2O.sub.3 18-25% Li.sub.2O 2.5-3.8% K.sub.2O 0-<1.0
Na.sub.2O 0-<1.0% ZnO 1.2-2.8% MgO 0.30-1.5% CaO 0-1% BaO 0-3%
SrO .sup. 0-1.4% TiO.sub.2 1.8-3.2% ZrO.sub.2 1.0-2.5%.
5. The display assembly of claim 1, wherein the glass-ceramic plate
comprises antimony and arsenic in amounts not exceeding 0.01% by
weight.
6. The display assembly of claim 1, wherein the glass-ceramic plate
comprises vanadium oxide in a weight content of between
0. 01% and 0.2%.
7. The display assembly of claim 1, wherein the glass-ceramic plate
comprises vanadium oxide in a weight content of between 0.01% and
0.03%.
8. The display assembly of claim 1, wherein the glass-ceramic plate
comprises cobalt oxide in an amount by weight of 0.12% or less.
9. The display assembly of claim 1, wherein the glass-ceramic plate
comprises tin oxide in an amount by weight of between 0.1% and
0.5%.
10. The display assembly of claim 1, wherein the glass-ceramic
plate comprises tin oxide in an amount by weight of between 0.2%
and 0.35%.
11. The display assembly of claim 1, wherein the glass-ceramic
plate contains no nickel oxide.
12. The display assembly of claim 1, wherein the glass-ceramic
plate comprises less than or equal to 0.01% by weight of chromium
oxide.
13. The display assembly of claim 1, wherein the glass-ceramic
plate comprises less than or equal to 0.1% by weight of manganese
oxide.
14. The display assembly of claim 1, wherein the polychromatic
light source is a polychromatic LED.
15. The display assembly of claim 1, wherein the polychromatic
light source is a polychromatic LED which emits with a first
emission peak between 430 and 470 nm and a second peak between 540
and 560 nm.
16. The display assembly of claim 15, wherein the second peak is of
lower intensity than the first peak.
17. The display assembly of claim 1, wherein the polychromatic
light source is a polychromatic LED comprising three monochromatic
sources, the intensities of which are regulated independently.
18. A hob, comprising the display assembly of claim 1 and a heating
element.
19. The display assembly of claim 1, wherein the glass-ceramic
plate comprises antimony and arsenic in amounts not exceeding
0.001% by weight.
20. The display assembly of claim 1, wherein the glass-ceramic
plate contains no antimony and arsenic.
Description
[0001] The invention relates to the field of glass-ceramics.
[0002] It relates more precisely to a display assembly comprising a
luminous device and a glass-ceramic plate of the lithium
aluminosilicate type.
[0003] Glass-ceramics are intended especially to be used as cooking
articles, in particular as hobs covering heating elements such as
halogen or radiant heating elements, or as cooking utensils.
[0004] Glass-ceramics of the lithium aluminosilicate type have
proved to be very suitable for these uses because of their esthetic
character, which can be varied widely, their mechanical properties,
especially their high impact strength due to their low thermal
expansion coefficient in the range of operating temperatures, and
their chemical properties, namely their resistance to both acids
and bases.
[0005] Conventionally, a glass-ceramic is produced in several
steps: a) melting of the batch materials containing at least one
nucleating agent; b) forming and cooling of the glass, called the
"mother glass"--at a temperature lower than its conversion range;
and c) heat treatment to ceramize the glass.
[0006] This "ceramization" heat treatment makes it possible, in one
of its embodiments, to grow within the glass crystals of
.beta.-quartz structure that have the particular feature of having
a negative thermal expansion coefficient.
[0007] The presence, in the final glass-ceramic, of such crystals
and of a residual glassy phase, makes it possible to obtain a zero
or very low overall thermal expansion coefficient (the absolute
value of the expansion coefficient is typically less than or equal
to 15.times.10.sup.-7/.degree. C., or even
5.times.10.sup.-7/.degree. C). The size of the .beta.-quartz
crystals is generally very small, typically between 30 and 70
nanometers, so as not to scatter visible light.
[0008] Glass-ceramics also possess specific optical properties that
depend on their usage. Thus, in the case of a hob, it is important
for the glass-ceramic to have low transmission for visible light so
that the user is unable to distinguish, or to do so only with
difficulty, the underlying heating elements when they are not
operating. However, at the same time the hob must allow the heating
elements to be seen when they are heating, without however dazzling
the user, so as to reduce the risk of being burnt on contact with
the hotplate. The glass-ceramic must also have good energy
transmission properties, in particular for infrared radiation
produced by the heating elements, in order to allow the food to be
heated to the desired temperature in the shortest possible time
period.
[0009] Current hobs are generally tinted using vanadium oxide.
Vanadium oxide is added to the batch materials of the mother glass
before the melting operation, and it gives, after ceramization, a
very pronounced brown-orange tint, due to reduction of the
vanadium.
[0010] Such glass-ceramics tinted solely using vanadium oxide
transmit the wavelengths lying within the red (above 600 nm), so
that the heating elements are visible when they are taken to high
temperature. The displays produced using light-emitting diodes (or
LEDs) emitting in the red are also visible through the hob and
therefore particularly suitable for this type of glass-ceramic.
[0011] For esthetic reasons, there has recently appeared a need
also to be able to see displays of different colors, something
which is especially difficult because of very low transmission
factors in the visible outside the red range for glass-ceramic
plates currently available commercially.
[0012] The aim of the invention is to alleviate the aforementioned
drawbacks with a display assembly 1 comprising, on the one hand, a
glass-ceramic plate 2 of the lithium aluminosilicate type, the
optical transmission of which for a thickness of 4 mm is between
0.2% and 4% for at least one wavelength between 400 and 500 nm and,
on the other hand, a luminous device 4, noteworthy in that the
luminous device 4 comprises at least one polychromatic light source
5 having at least a first emission of nonzero intensity at said
wavelength between 400 and 500 nm and at least a second emission at
a wavelength of more than 500 nm, and such that the positioning of
said source 5 is designed to allow display through said
glass-ceramic plate 2.
[0013] The display assembly according to the invention comprises a
plate, preferably a hob, intended to be integrated into a cooking
range, the latter comprising the hob and the heating elements, for
example radiant or halogen heating elements or induction heating
elements. The display is made through the plate using a
polychromatic luminous device that emits in a first wavelength of
400 to 500 nm and at least in a second wavelength above 500 nm. The
inventors have discovered, surprisingly, that the combination of
these various wavelengths emitted by the luminous device and their
respective absorptions through the glass-ceramic plate makes it
possible to display all the shades of color perceptible to the
human eye. Such a display assembly integrated into a cooking range
consequently provides an infinite number of shades in terms of
color and light intensity. Such an invention makes it possible to
produce a variety of animation effects on the cooking range by
associating, for example, spaces or functions with particular
colors.
[0014] The term "monochromatic light source" in the context of the
present invention defines a light source that has a single emission
peak in the visible wavelength range and such that the width of the
peak varies from 1 to 100 nm, preferably from 5 to 50 nm and even
10 to 30 nm.
[0015] The term "polychromatic light source" in the context of the
present invention defines a light source which has at least two
emission peaks in the visible wavelength range. It may be an LED
and/or a display based on one or more LEDs, with an emission
spectrum having a main emission peak and a fluorescence emission
peak, wider than the main peak and of lower intensity.
[0016] The optical transmission of the glass-ceramic plate of the
display assembly described above, for a thickness of 4 mm, is
preferably between 0.4% and 1.5% for at least a wavelength between
400 and 500 nm.
[0017] Advantageously, the optical transmission for a thickness of
4 mm is preferably between 0.2% and 4%, especially between 0.4% and
1.5%, for any wavelength between 400 and 500 nm.
[0018] Higher transmissions would result in the heating elements
being visible even outside heating periods, something which is to
be excluded. In the case of lower transmissions on the other hand,
the visibility of the blue or green displays would be too low.
[0019] The light transmission in the context of the ISO 9050 (2003)
standard and using the illuminant D.sub.65 is preferably less than
or equal to 3%, or less than or equal to 2% and even less than or
equal to 1% for a plate 4 mm in thickness. Thus, the heating
elements are not visible when they have been turned off.
[0020] The term "light transmission" is understood to mean the
total transmission, taking into account both direct transmission
and possible diffuse transmission. For example, a spectrophotometer
provided with an integrating sphere is therefore used, the
transmission measured at a given thickness then being converted to
the reference thickness of 4 mm using methods known to those
skilled in the art, including in particular the ISO 9050 (2003)
standard.
[0021] The expression "glass-ceramic of the lithium aluminosilicate
type" of the display assembly according to the invention is
preferably understood to mean a glass-ceramic that comprises the
following constituents, in the limits defined below expressed in
percentages by weight:
TABLE-US-00001 SiO.sub.2 52-75% Al.sub.2O.sub.3 18-27% Li.sub.2O
2.5-5.5% K.sub.2O 0-3% Na.sub.2O 0-3% ZnO 0-3.5%.sup. MgO 0-3% CaO
0-2.5 BaO 0-3.5%.sup. SrO 0-2% TiO.sub.2 1.2-5.5% ZrO.sub.2 0-3%
P.sub.2O.sub.5 0-8%.
[0022] This glass-ceramic may comprise up to 1% by weight of
non-essential constituents that do not affect the melting of the
mother glass or the subsequent devitrification that results in the
glass-ceramic.
[0023] Preferably, the glass-ceramic of the lithium aluminosilicate
type of the display assembly according to the invention comprises
the following constituents in the limits defined below, expressed
in percentages by weight:
TABLE-US-00002 SiO.sub.2 64-70% Al.sub.2O.sub.3 18-25% Li.sub.2O
2.5-3.8% K.sub.2O 0-<1.0% Na.sub.2O 0-<1.0% ZnO 1.2-2.8% MgO
0.30-1.5% CaO 0-1% BaO 0-3% SrO .sup. 0-1.4% TiO.sub.2 1.8-3.2%
ZrO.sub.2 1.0-2.5%.
[0024] The barium oxide content is preferably between 1 and 3%,
especially between 2 and 3%, so as to reduce the viscosity of the
glass. For the same reason, the silica content is preferably less
than or equal to 68%, especially 67% or even 66%. The inventors
have also been able to demonstrate that there is a very pronounced
effect of the lime (CaO) content on the reduction in viscosity,
even for very small amounts added. For this reason, the CaO content
is at least 0.2%, especially 0.3% and even 0.4%.
[0025] The best results are obtained for alumina (Al.sub.2O.sub.3)
contents of 23% or less, especially 20.5%.
[0026] To achieve the desired optical properties, colorants are
added to the composition. Thus, the chemical composition of the
plate of the display assembly according to the invention preferably
comprises vanadium oxide having a weight content of between 0.01%
and 0.2%. This content is even preferably less than or equal to
0.05%, or 0.04% or 0.03% or even 0.025% or 0.02%. The preferred
vanadium oxide contents are between 0.01 and 0.03%.
[0027] High vanadium oxide contents darken the plate and
consequently result in poor visibility of the display, in
particular in the blue. Lower contents on the contrary lighten the
hob.
[0028] To conceal the heating elements well, the plate according to
the invention may furthermore contain, especially in combination
with vanadium oxide, the following coloring agents within the
following weight ranges:
TABLE-US-00003 Fe.sub.2O.sub.3 0-1%; NiO 0-1%; CuO 0-1%; CoO 0-1%;
MnO 0-1%.
[0029] Preferably the cobalt oxide content in the composition of
the glass-ceramic plate of the display assembly according to the
invention is less than or equal to 0.12% or even 0.02%.
[0030] The sum of the percentage contents of these coloring agents
(Fe.sub.2O.sub.3, NiO, CuO, CoO and MnO) is less than or equal to
0.025%, preferably at least equal to 0.045%, but does not exceed
2%. Preferably, the hob of the display assembly according to the
invention does not however contain nickel oxide, including when the
vanadium content is between 0.01% and 0.03%. Chromium oxide
(Cr.sub.2O.sub.3) is an impurity frequently found in most batch
materials, in particular in titanium-containing compounds of the
rutile type. Furthermore, certain refractories from which melting
furnaces are made may contain chromium oxide or consist of chromium
oxide. To obtain the desired properties, it is preferable for the
chromium oxide (Cr.sub.2O.sub.3) weight content in the plate of the
display assembly according to the invention to be less than or
equal to 0.01%, preferably 0.0075% or even 0.006%. Limitation to
such low contents means that the batch materials must be carefully
selected and the presence of chromium oxide refractories in contact
with the molten glass has to be avoided.
[0031] Preferably, the manganese oxide (MnO) weight content in the
plate of the display assembly according to the invention is less
than or equal to 0.1%, preferably 0.045% or even 0.025%.
[0032] The chemical composition of the plate of the display
assembly according to the invention may comprise tin oxide in an
amount by weight of between 0.1% and 0.5%, since tin oxide helps to
promote vanadium reduction during the ceramization step, causing
the appearance of color. It also helps to refine the mother glass
during the melting thereof, that is to say it helps to promote the
elimination of gaseous inclusions within the mass of molten glass.
Other reducing agents than tin have proved to be even more
effective, especially metal sulfides, as explained in greater
detail in the rest of the text. The chemical composition of the hob
of the display assembly according to the invention may therefore
advantageously contain tin oxide with a weight content of between
0.2% and 0.35%.
[0033] The chemical composition of the plate of the display
assembly according to the invention contains at most small amounts
of antimony and arsenic (i.e. in amounts not exceeding 0.01% by
weight, or even 0.001%), for environmental reasons and because it
has proved difficult to make these oxides compatible with a forming
process of the float type, in which the molten glass is poured onto
a bath of molten tin.
[0034] Preferably, the chemical composition of the plate according
to the invention contains no antimony and arsenic.
[0035] The chemical composition of the plate of the display
assembly according to the invention may optionally comprise
phosphorus oxide (P.sub.2O.sub.5) and/or rubidium oxide (Rb.sub.2O)
having weight contents of less than or equal to 0.1%, preferably
0.09% or even 0.07%.
[0036] The glass-ceramic of the display assembly according to the
invention preferably comprises crystals of .beta.-quartz structure
within a residual glassy phase. The absolute value of its expansion
coefficient is typically less than or equal to
15.times.10.sup.-7/.degree. C. or even 5.times.10.sup.-7/.degree.
C.
[0037] Preferably, the polychromatic light source of the display
assembly as described above is a polychromatic LED and/or a display
based on one or more polychromatic LEDs.
[0038] Such an LED (and/or such a display based on one or more
LEDs) provided as light source for the display assembly according
to the present invention is polychromatic and possesses an emission
spectrum comprising at least two peaks at different wavelengths. As
a result, the color perceived by the observer through the plate is
a mixture of the various wavelengths transmitted by the plate.
[0039] The inventors have discovered, surprisingly, that adjusting
the emission spectrum of commercial polychromatic LEDs (or choosing
the LED (and/or the display based on one or more LEDs) that give
the best compromise directly), in combination with the fixed
transmission spectrum of the glass-ceramic plate used in the
display assembly, makes it possible to obtain color displays
substantially throughout the range of the visible spectrum. The
LEDs and/or displays based on LEDs are particularly suitable for
this type of use, provided that they provide a multitude of
emission spectra according to the chosen adjustment. The choice of
source as a function of the desired illumination through the plate
will be explained further below.
[0040] Advantageously, the polychromatic LED (and/or the display
based on one or more LEDs)) emits with a first emission between 400
and 500 nm and with a second emission above 500 nm. LEDs commonly
called "hybrid LEDs" (electroluminescent crystal+photoluminescent
phosphor(s)) enable such emission spectra to be obtained. Such
LEDs, the spectrum of which has a very broad secondary emission,
are easy to obtain commercially. The white LEDs used in the context
of the invention are for example manufactured from a semiconductor
crystal chip, such as one made of indium gallium nitride (InGaN)
emitting in the blue covered with a transparent (silicone or epoxy)
resin containing inorganic luminophores (for example YAG:Ce), which
absorbs the blue and emits in the yellow. The following LEDs or
displays based on LEDs may also be mentioned: [0041] the XLamp.RTM.
LED range of "High Brightness LED" from the company CREE (USA);
[0042] the following ranges: NichiaHelios, NichiaRigel, "LED-lamp",
NSSM, NSSW, NSEW, NS9 and NS2 references from the company Nichia
(Japan); [0043] the series of white "TOPLED.RTM." from the company
OSRAM (Germany); [0044] the "Luxeon.RTM. Rebel White" and
"Luxeon.RTM. K2" range from the company Philips Lumileds (USA); and
[0045] the LEDs with the following references: E1S19, E1S27, E1S62,
E1S66, E1S67, E1SAG, E1SAP, EASAA, EASAU, EASAV, E1L4x and E1L5x
from the company Toyoda Gosei (Japan).
[0046] Displays based on one or more LEDs are luminous display
devices, the "primary" light source of which consists of one or
more LEDs, usually covered with a diffusing element. These devices,
intended for displaying alpha-numeric symbols/words, are generally
composed of luminous "segments" (for example 7-segment displays),
dots (matrix displays) or bars. The following displays based on one
or more LEDs may be mentioned: [0047] white 7-segment displays of
the HDSM-431W and HDSM-433W references from the company Avago
Technologies (USA); [0048] "Dot Matrix.RTM." matrix displays from
the company KingBright, for example with the reference TA20-11YWA;
[0049] "Bar Graph Array.RTM." bar displays from the company
KingBright, for example with the reference DC10YWA.
[0050] It is also possible to use LEDs with an emission of high
intensity in the visible beyond 500 nm and with a narrower emission
peak, but of lower intensity, between 400 and 500 nm.
[0051] Preferably, the polychromatic light source of the luminous
device of the display assembly described above is a polychromatic
LED (and/or a display based on one or more LEDs) which emits with a
first emission peak between 430 and 470 nm (limits inclusive),
preferably 450 nm, and a second peak between 540 and 560 nm (limits
inclusive), preferably 555 nm. Such a source, suitably regulated,
makes it possible to obtain a white display through the
glass-ceramic plate of the display assembly described above. By
producing such a white display through an essentially dark brown
glass-ceramic plate makes it possible to achieve particularly
desirable luminous effects in terms of design.
[0052] Advantageously, the polychromatic LED (and/or the display
based on one or more LEDs) emits with a first emission peak at
between 430 and 470 nm, preferably 450 nm, and a second peak at
between 540 and 560 nm (limits inclusive), preferably 555 nm, the
second peak being advantageously of lower intensity than the first.
The inventors have shown that, with the glass-ceramic plates used,
such LEDs (or display) would allow the best color rendition of
white displays.
[0053] Preferably, the polychromatic light source of the luminous
device of the display assembly described above is a polychromatic
LED (and/or display based on one or more LEDs) consisting of three
monochromatic sources (the sources may be in the same LED or may be
three independent monochromatic LEDs), the intensities of which are
designed to be adjusted independently: such LEDs (often called
"RGB" LEDs), for example consisting of three different sources each
having the emission spectrum of one of the three primary colors
(red, green and blue), provides an emission spectrum personalized
according to the desired application in terms of coloration and
light intensity through the glass-ceramic plate.
[0054] The light source of the luminous device of the display
assembly according to the present invention may also comprise,
individually or in combination with the light sources described
above, any type of display, such as displays based on LEDs
(seven-segment displays, matrix displays, etc.).
[0055] The flux emitted by the LED and/or the display based on one
or more LEDs (in the visible) is adapted to the desired luminance
(light) level through the glass-ceramic plate, given the spectrum
of the LED (and/or the display) and the spectral transmission (in
the visible) of the plate. A person skilled in the art of LED-based
light displays knows how to vary the parameters of the source in
order to obtain the desired luminance.
[0056] The invention also relates to a method of adjusting and/or
selecting at least one light source of the polychromatic luminous
device of the display assembly as described above.
[0057] For a set of N (N.gtoreq.2) glass-ceramic plates, the method
comprises the following steps:
[0058] 1) define the color coordinates (x.sub.c, y.sub.c) of the
target (according to the CIE 1931 model) for a display with a
chosen shade of color in transmission through the N glass-ceramic
plates;
[0059] 2) choose the spectrum and calculate the color coordinates
(x.sup.r.sub.s, y.sup.r.sub.s) of an adjustment polychromatic
source which, in transmission through the N plates, gives an
average color rendition substantially close to the target color
rendition (x.sub.c, y.sub.c); and
[0060] 3) minimize the distance between the set of color
coordinates (x.sup.i.sub.t, y.sup.i.sub.t) of the glass-ceramic
plate and the average color coordinates ( x.sub.t, y.sub.t) for N
glass-ceramic plates, while keeping the distance between the
average color coordinates ( x.sub.t, y.sub.t) for N glass-ceramic
plates and the color coordinates (x.sub.c, y.sub.c) of the target
below a value acceptable for the intended application.
[0061] For one glass-ceramic plate (N=1), the method comprises the
following steps:
[0062] 1) define the color coordinates (x.sub.c, y.sub.c) of the
target (according to the CIE 1931 model) for a display with a
chosen shade of color in transmission through the glass-ceramic
plate;
[0063] 2) choose the spectrum and calculate the color coordinates
(x.sup.r.sub.s, y.sup.r.sub.s) of a polychromatic source which, in
transmission through the plate, gives an average color rendition
substantially close to the target rendition (x.sub.c, y.sub.c);
and
[0064] 3) minimize the distance between the color coordinates
(x.sub.t, y.sub.t) of the source through the glass-ceramic plate
and the color coordinates (x.sub.c, y.sub.c) of the target.
[0065] The inventors have demonstrated that the most appropriate
solution for selecting a light source, so as to obtain a display
with a certain color and with the desired shade, firstly consists
in defining, in the CIE 1931 color diagram, the perceived color as
a function of the color coordinates (x, y).
[0066] The method described above serves to obtain a substantially
identical display for a group of N different glass-ceramic plates
using the same source. This method is also useful for determining
which light source gives a color rendition substantially identical
for each plate of a given type, despite the differences in
structure and composition of the material due to the manufacture.
In other words, step 3) serves to obtain the same color rendition
for N different plates or to take into account the manufacturing
tolerances for a given plate.
[0067] The target, that is to say the display through the plate, in
terms of color rendition, has the color coordinates (x.sub.c,
y.sub.c). Having defined the color coordinates (x.sub.c, y.sub.c)
of the "target" display, the aim is to determine the color
coordinates (x.sub.s, y.sub.s) of the polychromatic source for
obtaining the desired color rendition through the plate.
[0068] A set of N glass-ceramic plates, the chemical compositions
and the optical transmissions of which are such as described above
for the display assembly according to the invention, is
considered.
[0069] Let (x.sup.i.sub.t, y.sup.i.sub.t) be the color coordinates
of the color rendition obtained in transmission through plate i (i
ranging from 1 to N), using the adjustment polychromatic source
that emits substantially within the entire visible wavelength range
and has the color coordinates (x.sup.r.sub.s, y.sup.r.sub.s). Thus
an area in the CIE 1931 diagram in which the N color coordinates
(x.sup.i.sub.t, y.sup.i.sub.t) are located is defined.
[0070] Let ( x.sub.t, y.sub.t) be the color coordinates of the
average color transmitted through the N glass-ceramic plates, the
mathematical expression for which is given below:
x t _ = 1 N i = 1 N x t i ; y t _ = 1 N i = 1 N y t i ( i )
##EQU00001##
[0071] To have an identical color rendition of the display in
transmission through the N glass-ceramic plate selected, for
example a white color rendition, the aim is to make the size of the
area in the CIE 1931 diagram where the N color coordinate points
(x.sup.i.sub.t, y.sup.i.sub.t) (i ranging from 1 to N) are located
as small as possible. This may be achieved by minimizing the
quantity:
1 N i = 1 N ( x t i - x _ t ) 2 + ( y t i - y _ t ) 2 ( ii )
##EQU00002##
[0072] To obtain a defined color, for example white, the aim is to
make the distance between the average color coordinates ( x.sub.t,
y.sub.t) for the N glass-ceramic plates and the color coordinates
(x.sub.c, y.sub.c) of the target, in the CIE 1931 chromaticity
diagram, smaller than an acceptable limit value depending on the
intended application.
[0073] This distance may be calculated/evaluated/estimated by means
of the following equation:
{square root over (( x.sub.t-x.sub.c).sup.2+(
y.sub.t-y.sub.c).sup.2)} (iii)
[0074] The limit value chosen will be 0.05, preferably 0.01 and
even more preferably 0.005.
[0075] Using equations (ii) and (iii) to carry out step 3) of the
method, the color coordinates (x.sub.s, y.sub.s) of the sources
that can be used to obtain the desired luminous effect are then
known.
[0076] The subject of the invention is also a hob comprising a
display assembly as described above and at least one heating
element, for example a radiant or halogen heating element or an
induction heating element.
[0077] The invention will be better understood in the light of the
examples, together with the appended drawings and graphs, given
solely by way of illustration, which must in no way be interpreted
as being limiting, in which:
[0078] FIG. 1 shows, seen side-on and in cross section, one
embodiment of a display assembly according to the present
invention;
[0079] FIGS. 2 and 3 represent the optical transmission spectrum of
various glass-ceramic plates used in a display assembly according
to the present invention (FIG. 3 is an enlargement of the spectrum
shown in FIG. 2). In the graph, the percentage amount of light
transmitted by the plate is plotted on the y-axis as a function of
the wavelength, in nanometers, of the transmitted beam, given on
the x-axis;
[0080] FIGS. 4, 6, 8, 10 and 12 represent the emission spectrum of
an example of polychromatic LEDs of a display assembly according to
the invention. In these figures, relative emitted light intensity
with respect to the maximum, taken as equal to 1, is plotted on the
y-axis as a function of the wavelength, in nanometers, of the
incident beam, given on the x-axis;
[0081] FIGS. 5, 7, 9, 11 and 13 represent the spectrum of the
radiation transmitted by the polychromatic LEDs, the emission
spectra of which are illustrated in FIGS. 4, 6, 8, 10 and 12
respectively, through the glass-ceramic plates having the
transmission spectra shown in FIGS. 2 and 3. In these FIGS. 5, 7,
9, 11 and 13, the relative transmitted light intensity with respect
to the maximum, taken as equal to 1, is plotted on the y-axis as a
function of the wavelength, in nanometers, of the transmitted beam,
given on the x-axis; and
[0082] FIG. 14 shows the spectrum of the radiation emitted by a
polychromatic LED obtained through two glass-ceramic plates of
different composition. The dotted curve corresponds to the emission
of the LED selected at the start in order to carry out the
calculations. An identical display through two plates is obtained
with the spectrum corresponding to the solid curve.
[0083] The display assembly 1 shown in FIG. 1 comprises a
glass-ceramic plate 2 of chemical composition 3a, 3b, 3c or 3d, and
a luminous device 4 comprising a polychromatic source 5 (consisting
of an LED 6a, 6b, 6c, 6d or 6e) and a control means 7. In
operation, the polychromatic source 5 emits a light beam that
passes through the plate 2 in the display zone 8. The distance
between the source 5 and the plate 2 is less than or equal to 5 mm,
and may especially be less than 2 mm or even 1 mm.
[0084] The beam emitted by the source 5 has a width of between 0
and 5 mm. In the present case, the width of the beam is greater
than 0.5 mm.
[0085] Table 1 gives the chemical compositions C1, 3a, 3b, 3c and
3d of various glass-ceramic plates 2, indicating the percentage
contents by weight of the oxides.
[0086] Composition C1 (comparative example) is the chemical
composition of a glass-ceramic plate having very low transmissions
between 400 and 500 nm, resulting in practically zero visibility of
the LEDs that emit only within this range of the spectrum (blues to
green . . . ).
[0087] Compositions 3a to 3d are examples of the chemical
composition of the glass-ceramic plate 2 of the display assembly 1
according to the invention.
TABLE-US-00004 TABLE 1 C1 3a 3b 3c 3d SiO.sub.2 68.7 65.5 65.5 65.5
64.7 Al.sub.2O.sub.3 18.9 20.3 20.3 20.3 20.45 Li.sub.2O 3.5 3.8
3.8 3.8 3.75 TiO.sub.2 2.6 2.9 2.9 2.9 3.02 ZrO.sub.2 1.7 1.3 1.3
1.3 1.35 ZnO 1.6 1.5 1.5 1.5 1.52 MgO 1.3 0.4 0.4 0.4 0.36 CaO --
0.5 0.4 0.4 0.44 BaO 0.8 2.6 2.6 2.6 2.5 Na.sub.2O 0.1 0.6 0.6 0.6
0.62 K.sub.2O 0.1 0.2 0.2 0.2 0.25 MnO -- 0.02 0.02 0.02 --
SnO.sub.2 -- 0.3 0.3 0.3 0.25 V.sub.2O.sub.5 0.2 0.028 0.028 0.028
0.025 Fe.sub.2O.sub.3 0.1 0.1 0.1 0.1 0.087 As.sub.2O.sub.3 0.4 --
-- -- <0.01 Sb.sub.2O.sub.3 -- -- -- -- <0.01 Cr.sub.2O.sub.3
-- 0.0054 0.0017 0.0012 -- CoO -- -- -- 0.0147 -- P.sub.2O.sub.5 --
-- -- -- 0.07 Rb.sub.2O -- -- -- -- 0.09 B.sub.2O.sub.3 and/or F --
-- -- -- <0.01 White LED Zero Good Good Good Good visibility
[0088] Table 1 gives compositions of glass-ceramic plate specimens
3a, 3b, 3c and 3d, of the display assembly 1 for which white
displays are obtained. The transmission spectra given in FIGS. 5,
7, 9, 11 and 13 show that a white display is obtained by using the
appropriate LEDs (LEDs 6a to 6e), the spectral emission
characteristics of which are given in FIGS. 4, 6, 8, 10 and 12.
Emission of the Transmission Spectra Measurement Protocol
[0089] The various glass-ceramic plates are measured on specimens
measuring 50 mm.times.50 mm, the textured (pimpled) face of which
was removed by thinning/polishing the specimen. The measurement is
carried out by means of a spectrophotometer, for example a Perkin
Elmer Lambda950 spectrophotometer. The emission of the transmission
spectra are measured using an integrating sphere (for example a
SphereOptics SPH-12-X integrating sphere) coupled to a
spectrophotometer (for example an Instrument Systems CAS140
spectrophotometer).
[0090] FIGS. 2 and 3 show the transmission spectra of the plates
having the compositions C1, 3a, 3b, 3c and 3d given in Table 1. The
specimens of plates 2 of compositions 3a to 3d all have a
relatively high optical transmission between 400 and 500 nm,
compared with the specimen of plate 2 of composition C1. This is
because composition C1 is typically that of plates normally used in
cooking ranges that transmit well only for wavelengths in the
red.
[0091] FIGS. 4, 6, 8, 10 and 12 show the emission spectrum of an
example of polychromatic LEDs 6a to 6e of the luminous device 4 of
the display assembly 1. These LEDs were selected so as to obtain a
white color rendition of the display through the glass-ceramic
plate 2. These LEDs 6a to 6e all have in particular a first
emission peak with a maximum between 400 and 500 nm and a second
emission peak with a maximum between 500 and 650 nm.
[0092] FIG. 4 shows the normalized emission spectrum of the LED 6a,
the characteristics of which are the following:
[0093] Blue peak: [0094] Intensity=1.0 (unitless) [0095]
Position=450 nm [0096] Width=20 nm
[0097] "Yellow" peak: [0098] Intensity =0.22 (unitless) [0099]
Position=540 nm [0100] Width=93 nm.
[0101] This spectrum has the CIE 1931 color coordinates
x.sub.s=0.211; y.sub.s=0.219.
[0102] The normalized spectrum transmitted from the LED 6a through
the glass-ceramic plate specimen of composition 3b is plotted in
FIG. 5. This spectrum has the color coordinates x.sub.t=0.335 and
y.sub.t=0.339, giving a "white" color rendition of the LED display
through the glass-ceramic plate in question.
[0103] FIG. 6 shows a normalized emission spectrum of the OSRAM LED
with the reference LUW-G5AP "Ultra-White" (LED 6b). This spectrum
has the following characteristics:
[0104] Blue peak: [0105] Intensity=1.0 (unitless) [0106]
Position=432 nm [0107] Width=20 nm
[0108] "Yellow" peak: [0109] Intensity=0.13 (unitless) [0110]
Position=555 nm [0111] Width=105 nm.
[0112] This spectrum has the CIE 1931 color coordinates
x.sub.s=0.230; y.sub.s=0.180.
[0113] The normalized spectrum transmitted from the LED 4b through
the glass-ceramic plate specimen of composition 3c is plotted in
FIG. 7. The transmitted spectrum has the color coordinates
x.sub.t=0.356 and y.sub.t=0.263, giving a "pinky white" color
rendition of the LED through the glass-ceramic plate in
question.
[0114] FIG. 8 shows the normalized emission spectrum of an RGB LED
6c, the characteristics of which are the following:
[0115] Blue peak: [0116] Intensity=1.0 (unitless) [0117]
Position=460 nm [0118] Width=20 nm
[0119] Green peak: [0120] Intensity=0.47 (unitless) [0121]
Position=525 nm [0122] Width=35 nm.
[0123] Red peak: [0124] Intensity=0.11 (unitless) [0125]
Position=630 nm [0126] Width=15 nm. This spectrum has the CIE 1931
color coordinates x.sub.s=0.184; y.sub.s=0.250.
[0127] The normalized spectrum transmitted from the LED 6c through
the glass-ceramic plate specimen of composition 3b is plotted in
FIG. 9. The transmitted spectrum has the color coordinates
x.sub.t=0.335 and y.sub.t=0.338, giving a "white" color rendition
of the LED through the glass-ceramic plate in question.
[0128] FIG. 10 shows a normalized emission spectrum of the OSRAM
RGB LED with the reference LRTD-C9TP (LED 6d). This spectrum has
the following characteristics:
[0129] Blue peak: [0130] Intensity=1.0 (unitless) [0131]
Position=453 nm [0132] Width=25 nm
[0133] Green peak: [0134] Intensity=0.38 (unitless) [0135]
Position=520 nm [0136] Width=33 nm
[0137] Red peak: [0138] Intensity=0.07 (unitless) [0139]
Position=632 nm [0140] Width=18 nm.
[0141] This spectrum may be obtained with said LED by independently
controlling the current with which each of the chips (R, G, or B)
is supplied. By so doing, the spectrum of the LED has the CIE 1931
color coordinates x.sub.s=0.173; y.sub.s=0.185.
[0142] The normalized spectrum transmitted from the LED 6d through
the glass-ceramic plate specimen of composition 3a is plotted in
FIG. 11. The transmitted spectrum has the color coordinates
x.sub.t=0.337 and y.sub.t=0.332, giving a "white" color rendition
of the LED through the glass-ceramic plate in question.
[0143] FIG. 12 shows a normalized emission spectrum of the
7-segment LED display from Avago Technologies (reference HDSM-431W)
(LEDs 6e). This spectrum has the following characteristics:
[0144] Blue peak: [0145] Intensity=1.0 (unitless) [0146]
Position=455 nm [0147] Width=20 nm
[0148] "Yellow" peak: [0149] Intensity=0.3 (unitless) [0150]
Position=551 nm [0151] Width=108 nm. This spectrum has the CIE 1931
color coordinates x.sub.s=0.250; y.sub.s=0.270. The normalized
spectrum transmitted from the LED system 6e through the
glass-ceramic plate specimen of composition 3d is plotted in FIG.
13. The transmitted spectrum has color coordinates x.sub.t=0.401
and y.sub.t=0.353, giving an "orangey-white" color rendition of the
LEDs through the glass-ceramic plate in question.
[0152] FIG. 14 shows a result obtained by applying the method of
adjusting and/or selecting a light source. The plate specimens from
which the calculations were made are the two glass-ceramic plates
of composition 3b and 3d. The dotted curve represents the initial
normalized emission spectrum of the LED used at the start of the
method of selecting a light source. The solid curve represents the
normalized final emission spectrum of the LED obtained at the end
of the method. The acceptable limit value, as defined in step 3 of
the method, is taken as 0.01.
The characteristics of these spectra are the following:
Initial Spectrum
[0153] Blue peak: [0154] Intensity=1.0 (unitless) [0155]
Position=450 nm [0156] Width=20 nm
[0157] "Yellow" peak: [0158] Intensity=0.50 (unitless) [0159]
Position=555 nm [0160] Width=100 nm
Final Spectrum
[0161] Blue peak: [0162] Intensity=1.0 (unitless) [0163]
Position=4660 nm [0164] Width=10 nm
[0165] "Yellow" peak: [0166] Intensity=0.25 (unitless) [0167]
Position=542.9 nm [0168] Width=98.5 nm.
[0169] The predictions made beforehand by the calculations, in
accordance with the method of selecting the light source of the
polychromatic luminous device of the display assembly according to
the invention are therefore confirmed.
* * * * *